Automatic speed control safety valve for hydraulic elevators



s Hw M T SW L GE 0 m Aw JH June 13, 1961 AUTOMATIC SPEED CONTROL SAFETY VALVE FOR Filed Nov. 21, 1958 2 Sheets-Sheet 1 June 1961 D. J. ARBOGAST ET AL 2,988,050

AUTOMATIC SPEED CONTROL SAFETY VALVE FOR HYDRAULIC ELEVATORS Filed Nov. 21, 1958 2 Sheets-Sheet 2 PUM P 2,988,060 AUTGMATIC SPEED CONTROL SAFETY VALVE FOR HYDRAULIC ELEVATORS Duane .I. Arbogast, Olive Branch, Miss., and Lawrence F. Jaseph, Memphis, Tenn, assignors to Dover Corporation, Memphis, Tenn., a corporation of Delaware Filed Nov. 21, 1958, Ser. No. 775,591

7 Claims. (Cl. 121-464) The invention relates generally to hydraulic elevators, and more particularly to valve means for preventing overspeed descent of the elevator cab or cage, particularly in the event of the fracture of the pipe or conduit by which hydraulic fluid is supplied to and exhausted from the elevator jack.

It is an object of the invention to provide an improved valve for preventing overspeed lowering of the elevator cab or cage, by smoothly bringing it to a stop.

A further object is to provide a control valve which, whenever the speed of the elevator is unsafely rapid, will stop the descent of the cab gradually, without jarring of the personnel or apparatus within the cab.

It is a further object of the invention to provide a valve of the above mentioned type which does not offer appreciable resistance to flow of the hydraulic fluid to the jack cylinder as the elevator is being raised.

Other objects will become apparent from the following description, reference being had to the accompanying drawings, in which:

FIG. 1 is a partially quarter sectional view of the overspeed control valve of the invention;

FIG. 2 is in part an enlarged sectional view showing the resilient stop mechanism for limiting downward movement of the control valve;

FIG. 3 is a transverse sectional view, taken on the line 3-3 of FIG. 1;

FIG. 4 is a fragmentary sectional view of the needle valve and associated passageways by which the final deceleration of the downward movement of the elevator, as is approaches the stop, may be controlled;

FIG. 5 is a more or less schematic diagram of the system in which the improved overspeed valve of the invention may be used; and

FIG. 6 is a central vertical sectional view of a modified form of the invention.

The valve of the present invention serves to prevent lowering of a hydraulic elevator at a speed greater than one chosen as a safe maximum, closing entirely under such conditions to bring the elevator smoothly to rest, while interposing no appreciable resistance to the raising of the elevator, nor interfering with normal lowering. Such overspeed can occur by fracture of the pipe conveying the working fluid between the lifting jack and the pumping plant.

Referring to FIG. 5, the valve of the present invention is adapted to be used in a system in which the jack cylinder 10 has a plunger 12 freely reciprocable therein, the plunger having a cab or cage 14 secured to the upper end thereof. An overspeed preventing control valve 16 is directly and securely connected by bolts 17 to the jack cylinder 10 at one end, and its other end is connected by means of a pipe 18 to a three-way control valve 20, operated electromagnetically by depression of push button controls and associated circuitry. In one position the valve 20 directs the discharge of an electric motor driven pump 22 through a pipe 24, valve 20, pipe 18, and through the overspeed preventing control valve 16, to the jack cylinder 10, whereas in its other (lowering) position the pipe 18 is connected by the valve 20 and pipe 26 to a reservoir 28 from which the hydraulic fluid (oil) is supplied to the intake of the pump 22.

The valve 20 and pump 22 are controlled by push butatent ton switches located in the elevator cab and in the wall adjacent the landing stations so that the pump 22 is energized Whenever the elevator is to be raised, and its energization interrupted when the elevator cab has reached the desired floor level. Similarly, the valve 20 is electromagnetically controlled to move to a position connecting pipes 18 and 24 when the elevator is to be raised, and to position connecting pipes 18 and 26 when the elevator is to be lowered. Such control system except for the overspeed control valve 16, is shown and described in Lawrence F. Jaseph Patent No. 2,355,164, dated August 8, 1944.

The present invention is concerned particularly with the construction of the overspeed preventing control valve 16, the details of which are shown in FIGS. 1 to 4, and in a modified form in FIG. 6.

It is, of course, highly desirable in the operation of elevators that they descend at a safe speed, and that if such speed is exceeded, due to fracture of the pipe conveying the working fluid from the pump to the jack cylinder, or for any other reason, they approach stopping position at a smooth rate of deceleration, and that the means for accomplishing this does not introduce substantial resistance while the elevator is being raised, nor interfere with normal lowering of the elevator.

Referring to FIG. 1, a preferred form of overspeed preventing valve is disclosed as comprising a body 30 which may be a casting having a generally transverse partition 32 providing a finished valve orifice 34 and a finished cylindrical surface 36 for a reception of a piston operated valve designated generally as 38, and comprising a piston portion 40 reciprocable in the finished cylinder 36 and a valve portion 42 freely reciprocable in the finished opening 34 in the partition 32.

The valve part 42 is generally of cup shape and has a plurality of openings 44, for example twelve in number, which are formed by a V profile milling cutter cutting inwardly from the outer cylindrical surface of the valve so as to provide openings 44 of uniform width for an appreciable extent of their length, and then of gradually narrowing width so as initially to provide an aggregate cross sectional area for flow of the fluid past the valve when the valve is in open position, as shown in FIG. 1, and progressively to decrease the aggregate cross sectional area for the flow of the fluid as the valve moves upwardly (FIG. 1) for a substantial extent of its upward travel, and then gradually reduce the aggregate cross sectional area for the flow of the fluid as the valve approaches its fully closed position. The fully closed position is attained when an O-ring 46 abuts against the lower edge of the partition 32. It will be noted that some clearance between the outer cylindrical surface of the valve 42 and the surface 34 of the valve body is provided so that the valve may operate rather freely until the O-ring 46 engages the lower edge of the partition 32.

The piston valve structure 38 is normally held in its lower position, as shown in FIG. 1, by a precompressed coil spring 48, the upper end of which abuts a shoulder 50 within a hollow adjusting screw 56 (the adjustment of which does not change the degree of compression of the spring), while its lower end normally abuts a washer 58 secured against downward movement on a rod 60 by a snap spring washer 62. A shoulder 64 formed within the body of the piston valve structure 38 is normally held against the washer 58 by means, including a spring 84, hereinafter described in detail. The latter structure also has a hole 66 for receiving the rod 60 when the valve structure 38 is moved upwardly from the position shown in FIG. 1.

The rod 60 is secured to the hollow adjusting screw 56 by a pin 68 extending transversely through the adjusting screw and the rod 60. A sealing cap 70 is threaded over the upper end of the adjusting screw 56 and serves as a lock nut for holding the adjusting screw in set position, and also by virtue of a gasket 72 preventing leakage of oil from the valve structure as awhole. It may be noted that the upper end of the adjusting screw 56 is provided with flats for engagement with a wrench. A customary wire and soft metal sealing device 74 may be secured between the cap 70 and a cylinder head 76 to inhibit tampering with the adjustment of the screw 56. The head 76 is bolted to the body 30 of the valve and a suitable gasket 78 is provided to seal the joint.

The valve body 30 is attached to the jack cylinder by bolts 17 extending through a flange 80 and a complementary flange 82 welded to the jack cylinder 10, generally as shown in FIGS. 3 and 5, thus nearly certainly precluding fracture or leakage at this joint. The tendency of the piston valve structure to move downwardly under the influence of the precompressed, or preloaded, coil spring 48, before the expansion of this spring is limited by washers 58 and 62, is resisted, but not prevented, by a relatively weak coil spring 84 (FIG. 2) which surrounds a boss 86 extending downwardly from the lower portion of the valve 42. The upper end of the spring 84 abuts against the lower end surface of the Valve 42, while the lower end thereof engages a spring saddle 88 which is formed integrally with a rod 90 reciprocable in a bore 92. The extent of reciprocation of the rod 90 is limited by a roll-pin 94 which is held in the boss 86 and is engageable with the rod at the ends of a milled flat surface 96 extending longitudinally of the rod 90. The rod 90 is provided with a central longitudinally drilled hole 98 and a kerf 99 to form a passageway by which the hydraulic pressure within bore 92 with respect to that in the lower chamber 100 is equalized. This spring 84 serves to hold the shoulder 64 of the valve structure 38 in engagement with the washer 58, when the spring 48 has expanded to the extent limited by the washers 58 and 6-2.

An upper chamber 102 is connected to the pipe 18. As shown in FIG. 1, there is a port 104 connecting the chamber 102 with the cylinder '36 in a position such that when the piston portion of the valve 38 is in its normal position (as shown in FIG. 1), relatively free flow of the fluid between the cylinder 30 and the chamber 102 is permitted. A second passageway or duct 106 (FIG. 4) connects the cylinder 36 to the chamber 102, but flow through this passageway is restricted by an adjustable needle valve 108.

To cause the elevator cab to rise, the operator, by means of motor starting mechanism controlled by a push button or push buttons in the elevator cab or at one of the landing stations, energizes the electric motor driving the pump 22. The pump supplies fiuid under pressure to the valve structure shown in FIG. 1. The valve is electromagnetically positioned by the push button (whenever the elevator is to ascend) so that the output of the pump 22 flows through the valve at a controlled rate to provide smooth starting acceleration, and hence to the chamber 102 of the valve 16. The fluid flows through the ports 44 in the valve 42, into the chamber 100, and hence to the jack cylinder 10, applying suflicient pressure to the plunger 12 to elevate the cab 14 and its load.

The pressure drop caused by the slightly restricted flow through the valve ports 44 will cause the valve structure 38 to move downwardly against the force of the spring 84 until flow substantially ceases, whereupon the valve and piston structure 38 will be restored to the normal position shown in FIG. 1.

This fluid under pressure is also supplied through port 104 to the cylinder 36 for the piston 40 and the valve is thus held in open position by this pressure, as wall as by the spring 48. When the pressure drop due to flow past the valve 42 is relatively high, the piston and valve structure 38 moves downwardly against the force of spring 84, to provide more rapid upward travel to the floor level selected by the operated push button, whereupon,-by well 4 known electromagnetic means, the motor for the pump 22 is deenergized, the valve 20 is closed, the ascension of the cab is therefore stopped at the desired floor level, and the valve structure 38 is restored to the position shown in 'FIG. 1, by the spring 84.-

When a push'button in the cab is operated to call for descent of the cab to a lower floor level, the valve 20 is electromagnetically operated to connect pipes 18 and 26, thus permitting flow of the hydraulic fluid from the jack cylinder 10 through the valve 16, pipe 18, valve 20, pipe 26, to the reservoir 28,v due to the pressure in the jack cylinder resulting from the action of gravity on the cab and its load. a a 1 The valve 16 is provided to limit the rate of such flow of the hydraulic fluid from the jack cylinder 10 to the reservoir 28 and to stop the fluid flow when there is a pressure failure in the system between the valve 16 and the pumping plant. i

During lowering of the cab or cage 14 a pressure drop will result from flow of the hydraulic fluid through the openings 44 in the valve 42, and the pressure in chamber 102 will be less than that in chamber 100. By virtue of the fact that chamber 102 is connected to the cylinder 36 by the relatively large port 104, the effective pressures on the opposite ends of the piston and valve structure 33 will be such that a force will be applied thereto in an upward direction, against the counterforce of the spring 48. At normal lowering speeds this counter-force is adequate to prevent motion of valve 42 upwardly during lowering of the elevator, so that no interference with normal operation occurs.

If for any reason lowering occurs at greater than normal speed and there is a higher than normal rate of fluid flow from chamber to chamber 102, either because of rupture of the oil conduit 18 or overloading of the elevator 14, the excess pressure required to force the increased volume of liquid through ports 44 is applied to the lower end of valve 42, and this pressure will now exceed the bias of spring 48, causing the valve 42 to begin to move upwardly. Its upward end is subject to the pressure in chamber 36, which is the same pressure as that in outlet port B before valve motion commences. However, when the valve moves, liquid must be displaced out of cylinder 36, first through the port 104 and then (and at first simultaneously) past the restricting needle valve 108 and through the passage 106. The rise in pressure in cylinder 36 checks any abrupt movement of valve 42.

As valve 42 moves upward, the area of ports 44 open to flow is reduced, requiring increased pressure drop to maintain flow therethrough, and thereby increasing the pressure difference applied to the two ends of valve 42. Movement of the valve toward closed position also compresses the spring 48, tending to increase its strength. It is important that spring 48 be long and soft enough that the buildup of strength be smaller than the buildup of pressure due to flow restriction through the ports 44 as the valve closes, in order that the valve will not come to a position of equilibrium in some partly closed position. With proper selection of the spring 48, the valve will move gently but positively and relatively rapidly to the fully closed position, once sufficient pressure diiference exists to start it moving at all. The pressure drop through ports 44 continues to increase as the valve closes, approaching the total pressure due to the load sustained as the valve reaches the closed position.

When the valve is approximately half closed, the forward edge of piston 40 covers the port 104, leaving the passage 106 restricted'by the needle valve 108 as the only egress for liquid from cylinder 36, thus slowing the closing motion of valve 42. Shortly, the valve piston 38 contacts cylinder closure member 76, bringing it to rest. In' this position the O-ring member 46 engages the bore 34 of the valve seat, insuring closing of the orifice 34 and preventing leakage entirely, and so preventing further downward movement of the elevator cab. Upward movement of I the plunger, after the-assumed fracture in the pipelfi is repaired, is not prevented.

Likewise, if for any reason other than fracture of the pipe'18, as above suggested, the flow of the hydraulic fluid becomes so rapid as to cause an abnormal pressure drop across the valve 42, this valve will move upwardly to a position in which it is fully closed by the O-ring 46 and cooperating parts, so as smoothly and rapidly to stop descent of the elevator. If substantial equilibrium is restored with respect to pressure in chambers 1132 and 180, the valve 42 may again' be opened due to the force applied by the spring 48, but such movement will be limited to the predetermined normal position by virtue of the fact that the washer '58 is secured to the rod 60,

which is in turn secured by pin 68 with the adjusting screw 56, and further, by virtue of the fact that the spring 84 operates as a buffer and is capable of returning the valve 42, if it moves downwardly beyond the position shown in FIG. 1, to the position shown, with the shoulder 64 of the valve and piston structure 38 abutting against the washer 58. The valve will thus, under these conditions, be restored to normal position.

In view of the fact that the spring 48 is substantially stronger than the spring 84, the normal at rest position of the piston and valve structure 3-8 may be changed. If the adjusting screw 56 is turned to move it inwardly, the piston valve structure3 8 will be moved downwardly and the effective aggregate area of the orifices 44 will be increased so that under the abnormal conditions previously mentioned, a larger volume of fluid may flow through these openings 44 before a sufflcientpressure difference is produced to cause the piston to be forced upwardly against the counterforce of the precompressed spring 48. This condition is desired where the hydraulic jack 10 has a relatively large diameter and a correspondingly large fluid flow requirement, or where the rated speed is to be increased. It should be clear that the adjustment of the screw 56 determines the effective aggregate area of the openings 44 through which the fluid flows and thus determines the rated speed of the elevator in descending. It will be noted that independent of the particular adjustment of the screw 56, the force required to compress the spring 48 is initially the same.

When there is an appreciable pressure differential during descent of the cage 14 between the chambers 100 and 102, with the pressure in the latter-being smaller, the valve 16 will respond immediately due to outflow of fluid from the cylinder 36 through the unrestricted port 104. This prevents delay in action of'the valve 16 and prevents excessive downward speed of the cage 14 before the valve has closed far enough to be effective in speed control. This is very important where there is a rupture in the line downstream of the valve16.

The needle valve 108 in the passage 106 regulates the rate of deceleration of the elevator cage 14- by regulating the speed of that part of the valve travel which restricts speed, thus insuring safe, controlled, and smooth stopping of the cage 14 when that is required.

By the use of this valve, the descent of the elevator cage is limited so as to be a safe speed irrespective of the load carried by the elevator, and irrespective of whether there is a fracture in the pipe 18, or due to other causes adequate pressure is not maintained in the connecting pipe 18. This is because the valve structure 16 operates under the control of the differential pressures produced in response to fluid flow rate rather than solely to the pressureof the fluid in the jack 10, and such as may be developed at the pipe 18, because of friction of fluid flow to the reservoir.

The purpose of the valve structure is primarily to make the closure of the valve as quick as can be sustained comfortably, after the closing motion has commenced.

In the modified form of the invention shown in FIG. 6,

- approximately the results obtained by the invention shown in FIGS. 1-5 may be attained.

- lindricalbody having a head or cap 122 welded thereto at the upper end thereof and a cap 124 bolted to the lower end thereof, suitable sealing means being provided therefor.

A transverse partition 126 is welded to the cylindrical body 120, dividing the interior of the latter into two chambers 128 and 130. The chamber 128 is connected by a pipe 132 to the jack cylinder, while the chamber is connected by a pipe 134 to the pump, in the same manner as described with reference to the system shown in FIG. 5. A valve and piston structure 136 is reciprocable within a valve orifice 138 formed in the partition 126 and in a cylinder 140 formed within the cap 122. As in the previously described embodiment, the piston and valve structure 136 has a number of slots 142 formed in the lower end thereof.

The valve 136 is normally forced to the position shown by a helical coil spring 144 which is compressed between a collar 146 pinned to a rod 148, and a collar 150 bearing against the upper end of a hollow adjustment screw 152 locked in adjusted position by a nut 154. The position of the collar 146 with respect to the upper end of the ad justin-g screw 152 may be adjusted by virtue of the fact that the rod 148 is threaded in the adjusting screw 152 and that the relative adjustment of the rod and the adjusting screw 152 may be varied and locked in adjusted position by a lock nut 156. A sealing cap 158 is threaded on the adjusting screw 152 and forms a suitably gaskcted seal with the lock nut 154. This cap, in addition to preventing leakage from the valve body, inhibits tampering with the adjustments of the hollow adjusting screw 152 and the adjustment of the rod 148.

A relatively weak coil spring 160 bears against a washer 162 which in turn abuts against a shoulder on an adjusting screw 164 having a flattened wrench engaging portion 166. The screw 164 is held in adjusted position by a lock nut 16-8. A cap is provided for sealing purposes and for deterring tampering with adjustment of the screw.

The cap 122 is provided with a passageway 172 connecting the cylinder 140 and the chamber 128, a check valve 174 being provided to perm-it flow of the hydraulic fluid from the cylinder 140 to the chamber 128 and to prevent flow in the opposite direction. A passageway 176 also connects the chamber 138 with the cylinder 140, the flow of hydraulic fluid through this passageway being capable of regulation by a suitably locked and sealed needle valve 178.

The upward movement of the piston valve structure 136 is limited by its engagement with the lower end of the adjusting screw 164, while its downward movement is limited by engagement with the upper end of a hollow cylindrical stop member 180.

In operation, to elevate the lift, the pump is operated to supply fluid under pressure tothe chamber 130, and this fluid flows through the slots 142 into the chamber 128 and thence to the jack cylinder, forcing the plunger and ele vator cage upwardly.

If the aggregate area of the ports 142 is inadequate to pass this flow without excessive pressure drop, the drop is applied to the lower end of piston 136, tending to lift it against the light pressure of spring 160, the fluid in the cylinder 14! escaping freely past check valve 174 and duct 172. A larger portion of the ports 142 is thus made available for fluid flow. When the flow ceases, valve 136 will be returned to the position shown, due to the expan sion of spring 160, and fluid will enter the cylinder 140 through duct 176, past needle valve 178.

When lowering is desired, fluid is bled, by the customary control means, from the pipe 134 and the fluid may leave the cylinder of the jack through pipe 132, through the ports 142, to the pipe 134, to the control valve means.

. The drop in pressure required to maintain this flow through the ports 142 will cause the pressure in chamber 130 to be lower than that in the chamber 128. If the flow rate is excessive, the pressure drop will exceed that corresponding to the bias of the spring 144'. This differential pressure will cause flow of the hydraulic fluid through duct 176, past the needle valve 173, and as a result the piston and valve structure 136 will commence to move downwardly, further restricting the flow through the ports 142 and causing an increase in the pressure differential between the fluid in chamber 130 and that in chamber 128. Assuming this condition continues, the valve and piston structure will be moved downwardly to fully closed position, cutting off the flow of fluid and thereby bringing the lower side of the piston portion of the piston and valve structure 136 into engagement with the end of the limit stop tube 180. As long as the pressure in chamber 130 is abnormally low, the valve will remain fully closed. When pressure is restored in the pipe 134, the valve and piston structure will be restored to normal position shown, due to the expansion of spring 144 against the relatively weak spring 160, the flow from cylinder 140 being relatively free past the check valve 174.

This form of valve has two different adjustments for trip speed, one by the adjustment of the hollow adjustment screw 152 which determines the position of the valve and piston structure in its resting position, and the other being by the stop nut 156 and rod 148 which alters both the length and the effective strength of spring 144, as well as changing the resting position of the valve structure.

From the foregoing, it will appear that an excessive rate of descent of the elevator is prevented by gradual closure of the valve 136, so that the elevator decelera-tes gradually at a rate determined by the adjustment of the needle valve 178 until the valve closes fully. Thus, the elevator is brought smoothly to a stop position at which it will be held until pressure is restored in the pipe 134. Such operation of the elevator and the control valve of the invention occurs whenever there is a failure in the valve means which controls the flow from the jack cylinder to the reservoir through pipe 134, or whenever there is a fracture in the pipe 134 or conduits connected therewith. T he valve mechanism of FIG. 6 therefore provides a reliable safety means for controlling the rate of descent of the elevator upon the type of failures mentioned, and gradually, but definitely, brings the elevator to a stop under such conditions.

While we have shown and described preferred embodiments of the invention, it will be apparent that numerous variations and modifications thereof may be made without departing from the underlying principles of the invention. We therefore desire, by the following claims, to include within the scope of the invention all such variations and modifications by which substantially the results of the invention may be obtained through the use of substantially the same or equivalent means.

We claim:

1. For use in a hydraulic elevator control system having a vertical jack cylinder, means for supplying a hydraulic fluid under pressure from a reservoir to the jack cylinder and for permitting hydraulic fluid to flow from the jack cylinder to the reservoir, an elevator plunger freely reciprocable in the jack cylinder, the reciprocation of the plunger being adapted to raise and lower a structure adapted to carry a load, means for controlling the rate of descent of the elevator comprising, in combination, a valve body having an apertured partition dividing the interior of the body into two chambers, means connecting the first of said chambers to the means for supplying the hydraulic fluid under pressure and for returning it to the reservoir, means connecting the second of said chambers to the jack cylinder, means forming a cylinder at one end of the body, a piston and valve structure having its piston portion reciprocable in the cylinder and having its valve portion reciprocable in the aperture in the partition, said valve portion having ports the aggregate eflective area of which varies as the position of the valve with respect to the partition is changed,

spring means engaging the valve and piston structure normally holding the latter in a rest position in which the ports in the valve provide a substantial aggregate cross sectional area for the flow of fluid between the two chambers, a port connecting the first chamber with the cylinder located so that it will be covered by the piston as the latter is moved a certain distance against the force of the spring means from its normal rest position, a duct connecting the first chamber and the cylinder at all times, adjustable means to control the rate of fluid flow through the duct, and means for adjusting the spring means to determine the normal rest position of the piston and valve structure.

2. The combination set forth in claim 1, in which there are abutment means for engagement with the ends of the spring, one of the abutments being adjustable to a fixed position relative to the valve body and the other being in engagement and movable with the piston and valve structure.

3. The combination set forth in claim 2, in which the adjustable abutment for the spring includes a rod extending through the spring, and in which the rod forms a guide for the movable abutment for the spring.

4. The combination set forth in claim 2, in which resilient means applying a force to the valve and piston structure in a direction opposite to that applied thereto by said spring is eflfective to move the piston and valve structure to a position in which it engages the movable abutment for the spring.

5. The combination set forth in claim 4, in which means are provided to attach the resilient means to the piston and valve structure.

6. For use in a hydraulic elevator control system having a vertical jack cylinder, valve controlled means for supplying a hydraulic fluid under pressure from a reservoir to a jack cylinder and for permitting hydraulic fluid to flow from the jack cylinder to the reservoir, an elevator plunger freely reciprocable in the jack cylinder, the reciprocation of the plunger being adapted to raise and lower a platform, means for controlling the rate of descent of the elevator comprising, in combination, a valve body having an apertured partition dividing the interior of the body into two chambers, means connecting the first of said chambers to the means for supplying the hydraulic fluid under pressure and for returm'jng it to the reservoir, means connecting the second of said chambers to the jack cylinder, means forming a cylinder at one end of the body, a piston reciprocable in the cylinder, a sleeve valve secured to the piston and reciprocable in the aperture in the partition, said valve having ports the aggregate effective area of which varies as the position of the valve with respect to the partition is changed, spring means engaging the valve and normally holding the latter in a rest position in which the ports in the valve provide a substantial aggregate cross sectional area for the flow of fluid between the two chambers, a port connecting the first chamber B with the cylinder located so that it will be covered by the piston as the latter is moved a certain distance from its normal rest position, a duct connecting the first chamber and the cylinder at all times, adjustable means to control the rate of fluid flow through the duct, and means for adjusting the position of the spring means to determine the normal rest position of the valve.

7. For use in a hydraulic elevator system, a valve structure to limit and control the rate of descent of the elevator cab structure in the event of failure of the conduit by which the hydraulic fluid is supplied to the jack cylinder of the elevator, comprising a valve body having a partition dividing the valve structure into two chambers the first of said chambers being adapted to be connected alternatively to a source of fluid pressure and to a reservoir and the second of said chambers being adapted for connection to the jack cylinder, said partition providing a valve orifice, a piston and sleeve valve 9 structure, the valve portion of said structure being reciprocable in the orifice in the partition, a cylinder for cooperation with the piston portion of said valve structure, the valve structure having a plurality of openings the aggregate cross sectional area of which decreases as the valve portion of the structure is moved in a direction from the second chamber to the first chamber, adjustable resilient means normally holding the valve and piston structure in a position such that the openings in the valve structure provide a substantial aggregate area for the flow of hydraulic fluid, means forming a duct connecting the first chamber to the cylinder to permit equalization of the pressure in said cylinder with the pressure in the first chamber, a second duct means including an adjustable valve connecting the chamber B with the cylinder for the piston portion of the piston-valve structure having its opening in said cylinder beyond the opening of said first duct means, said piston and sleeve valve structure being operable upon a pressure diiferential in the first and second chambers due to the pressure drop resultant from flow of hydraulic fluid through the openings in the valve portion of said piston and valve structure to permit gradual closure of the sleeve valve due to escape of the operating fluid from the cylinder 110 the first chamber, the first duct means being located such as to be covered by the piston after the valve has been partially closed.

References Cited in the file of this patent UNITED STATES PATENTS 186,863 Meikle Jan. 30, 1877 1,555,851 Van Emon Oct. 6, 1925 2,227,629 Cannon Jan. 7, 1941 2,785,660 Jaseph Mar. 19, 1957 

